A data processing unit such as disk array unit used as an external memory of a computer is equipped with a UPS (uninterruptible power supply) against power failure or auxiliary energy source such as storage battery that backs up important loads such as cash memory.
Lately, a DC type UPS that supplies DC power to loads in case of power failure such as momentary stoppage or interruption of commercial power, that is, DC backup power supply has drawn attention. A known art on rack-mount type DC backup power supply includes one disclosed in Japanese Patent Laid-open No. 2003-309935. This document discloses an art for making slim (thinning) a DC backup power supply and installing it flat within a height (about 45 mm) of one unit size of the rack.